feat(v2): reject settlements that fail nostr attribution cross-check (S5 G5)

When LNbits' nostr-transport stamps `nostr_sender_pubkey` and
`nostr_event_id` onto Payment.extra (post aiolabs/lnbits PR #4), the
listener now cross-checks the signer against the resolved machine's
`machine_npub` before any distribution. Mismatch / absence / unparseable
pubkey → settlement is recorded with `status='rejected'` and the
reason in `error_message`, distribution is skipped.

Wire shape:

  bitspire.SettlementAttributionError + assert_nostr_attribution()
    Raises on absence, mismatch, or unparseable pubkey on either side.
    Normalises both `machine.machine_npub` (operator UI accepts hex
    or `npub1...`) and the stamped sender through
    `lnbits.utils.nostr.normalize_public_key` so the comparison is
    canonical-hex on both sides.

  tasks._handle_payment
    parse_settlement -> stamp nostr_event_id onto bitspire_event_id ->
    try assert_nostr_attribution: on failure, insert row with
    initial_status='rejected' + error_message, return without
    spawning process_settlement.

  crud.create_settlement_idempotent
    Now takes `initial_status` (required) and `error_message`.
    Normal path passes 'pending'; rejected path passes 'rejected'
    with the reason. Single-statement insert — no two-step pending->
    errored dance.

  crud.get_stuck_settlements_for_operator
    New `rejected` bucket alongside `errored` / `stuck_pending` /
    `stuck_processing`. Distinct because retry is wrong for these:
    the row was misrouted, not operationally failed.

  models.DcaSettlement.status enum extended with 'rejected'.
    Worklist response model carries the new bucket; API + UI plumbed
    end-to-end.

  static/js/index.js + templates/satmachineadmin/index.html
    New 'rejected' worklist bucket (deep-orange, gpp_bad icon).
    Force-reset button now scoped to stuck_pending / stuck_processing
    only — was 'not errored' which would have shown on rejected too.

10 unit tests in tests/test_nostr_attribution.py cover hex<->hex,
hex<->bech32, case-insensitivity, every absent variant, mismatch,
and unparseable on either side. All pass.

Closes the consumer-side of aiolabs/satmachineadmin#19 (G5).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/satmachineadmin/index.html

@@ -653,7 +653,7 @@
                            @click="confirmRetryFromWorklist(props.row)">
                       <q-tooltip>Retry distribution</q-tooltip>
                     </q-btn>
-                    <q-btn v-if="bucket.key !== 'errored'"
+                    <q-btn v-if="bucket.key === 'stuck_pending' || bucket.key === 'stuck_processing'"
                            flat dense size="sm" icon="local_fire_department"
                            color="red"
                            @click="confirmForceResetFromWorklist(props.row)">